Adhesive sheets having a support substrate applied a pressure-sensitive adhesive (adhesive agent) thereto have been conventionally used in a wide variety of fields because of its simplicity, specifically, because the sheets are easy to affix on adherends by pressing force. Meanwhile, plastic molded articles have been frequently used in recent years in accordance with the needs for lighter products. With this, use of adhesive sheets to be affixed on plastic molded articles has increased. Examples of the plastic molded article include those molded from resins such as polycarbonate, polymethyl methacrylate, polystyrene, and ABS.
When an adhesive sheet that has a support substrate having gas barrier properties (for example, an adhesive label) is affixed on the surfaces of such a plastic molded article for ornamentation and the like, gas may be generated from the plastic molded article to form air bubbles between the adhesive sheet and the plastic molded article, and thus swelling or lifting, that is, blisters may occur. Occurrence of such blisters impairs the appearance of the labels and significantly reduces the ornamental function as adhesive sheets.
To solve such problems, Patent Literature 1, for example, discloses an acrylic adhesive agent composition, as the adhesive agent composition, containing a copolymer prepared by radically polymerizing a (meth)acrylic acid ester, a carboxyl group-containing compound that can copolymerize, and a tertiary amine having a vinyl group.
Patent Literature 2 suggests a blister-resistant adhesive sheet using an adhesive agent prepared by blending an aziridine-based crosslinking agent to a copolymer of an acrylic acid ester having an alkyl group having 4 to 12 carbon atoms and 0.1 to 10% by weight of a polar monomer such as acrylic acid or 2-hydroxyethyl acrylate.
Additionally, Patent Literature 3 discloses an adhesive sheet that contains, as the components for forming an adhesive agent layer, an adhesive agent component and a curable component that is an acrylic monomer or oligomer. The curable component, however, may reduce the cohesive force of the adhesive agent layer, or may make the adhesive agent layer whitely turbid if having poor compatibility with the adhesive agent component.
Furthermore, Patent Literature 4 discloses an adhesive agent composition prepared by blending a resin composition having a specific molecular weight obtained by copolymerizing an alkyl(meth)acrylate ester having 1 to 12 carbon atoms and a carboxyl group-containing unsaturated monomer, with a resin composition having a specific Tg and a specific molecular weight obtained by copolymerizing one or more monomers selected from an alkyl(meth)acrylic acid ester or cycloalkyl(meth)acrylic acid ester having 1 to 20 carbon atoms, benzyl methacrylate, or styrene with an amino group-containing unsaturated monomer.
Furthermore, Patent Literature 5 discloses a blister-resistant adhesive agent composition prepared by blending a crosslinking agent having a glycidyl group to a copolymer having a specific molecular weight obtained by copolymerizing an alkyl(meth)acrylic acid ester having 1 to 12 carbon atoms as the main component, a styrenic monomer, a carboxyl group-containing unsaturated monomer, and an amino group-containing unsaturated monomer.
Patent Literature 6 discloses a resin composition polymerized in acetone and having a weight average molecular weight of 1.5 million or more and a ratio of the weight average molecular weight/the number average molecule weight of 4.0 or less.